But please implement a Pause-function - I simply died the first time I started it because I was too slow with building towers.Also, every time I tried to save money for the 2nd tier tower I simply died before I could build it And - make a way to sell towers for like 3/4 of their price - I used all slots up and couldn't build anything.

Nice game, maybe make the initial delay before enemies start to come a bit longer to give players more time to think about what they need to do. As mentioned above a way to remove/sell towers would be nice and a possible further development could be to have difficulties depending on how much money you start with at the beginning of every round. Also, the map was slightly misleading as to which path the enemies would take, such as a gap between the grey rocks, but that might be intentional.